I've been thinking about having a project with dual '328 MCU and using I2C for comm between the two. I did some Google searching and found this blog, where the builder made a shield with a second '328. My objective is to have a lot of I/O pins.

http://blog.makezine.com/2010/01/11/homebrew-dual-core-arduino/

Does the above tutorial look like the best way to approach such a project? Maybe I should build a single MCU project with a more powerful MCU, like an Arduino Mega?

It can be very convenient to use several microcontrollers in one project. For example, certain manufacturers sell LED displays with an ATmega328 as a display controller. I built a project with several of these displays plus an Arduino, in effect making a 5 "core" device.

In another project I built the Arduino has to handle two simultaneous tasks: a user interface (via encoders, buttons, IR, and LED displays) plus some timed loops running in parallel. I had to write some fairly complicated code to ensure the interface is responsive without affecting the accuracy of the timers. With hindsight the project would have been a lot easier with two Arduinos.

The communication method you use isn't important: it can be serial, I2C, SPI, or simple signalling via digital I/Os.

A more powerful chip can certainly reduce the need for multiple microcontrollers, but it's not necessarily an easier or even a cheaper solution.

Some of the more complicated projects I have in mind would benefit enormously from having a dual-MCU setup. I think it's a perfectly reasonable way of handling complex tasks if, like me, you lack the necessary coding skills to pull it off with a single high-end chip and aren't all that bothered about minimizing hardware costs for mass production One such idea was for an 80s style drum synth, and while the current "solution" is to use one MCU for all input control scanning and display twiddling and a whole other one for sample playback, I am sure a decent programmer could do the whole thing on a single processor.

I suppose it depends what you're better at. If you're more comfortable with complex hardware than tricky code, then two Arduinos (or equivalent) might be a good way of approaching a problem.

Thank you for the feedback gentlemen. CrossRoads, absolutely incredible looking boards on the page linked to in your signature.

Since I have the parts already and am an absolute beginner at this, I think I'll start off by exploring communication between two '328 MCUs and work my way up from there; one on my Uno the other on a breadboard.

While it is a neat project, I wouldn't call it dual core, since the usual definition of dual core is two processors inside the same chip that share physical memory (and possibility caches, possibly not).

Here's a dual '328 design I ruminated on a while back but never implemented.I have a dual '1284 done up too.I wouldn't mind ordering a set of boards if there was some other interest.About $4.50 a board to mail a single PCB out when they arrived.

I was also thinking about trying something like this only slightly different. Say have an Atiny 85 running/doing something as part of an entire assembly/sensor/module and having a pin or 2 output to a 328. Or have a 328 pin trigger the 85 to run some type of sketch.

Does this make any sense or does anyone see any big flaws with attempting this?

Here's a dual '328 design I ruminated on a while back but never implemented.I have a dual '1284 done up too.I wouldn't mind ordering a set of boards if there was some other interest.About $4.50 a board to mail a single PCB out when they arrived.

Very nice! You can count me in for one of the dual '328 pcb's if you have them made up. I might even take two